1. Field of the Invention
This invention relates to a charging member, an electrophotographic apparatus and a process cartridge.
2. Description of the Related Art
An elastic layer of a charging roller used in a contact charging system usually has an electrical conductivity of approximately from 1×103 to 1×107 Ω·cm in volume resistivity. In order to obtain an elastic layer having such an electrical conductivity, an electronic conduction type conductive rubber composition compounded with conductive particles such as carbon black may be used to form the elastic layer. This is disclosed in Japanese Patent Application Laid-open No. H09-090714 and Japanese Patent Application Laid-open No. 2000-063656.
However, the elastic layer thus formed has, as disclosed in Japanese Patent Application Laid-open No. H09-090714 and Japanese Patent Application Laid-open No. 2000-063656, a problem that its electrical resistance depends so strongly on the state of dispersion of the conductive particles as to tend to cause resistance non-uniformity in the charging roller. In addition, in the charging member having such an elastic layer, the conductive particles in the elastic layer may faster come to aggregate because of continuous application of direct-current voltage, so that the elastic layer may gradually change in its electrical resistance.
Japanese Patent Application Laid-open No. 2007-292298 discloses that a bead mill may be used when the conductive particles such as carbon black are dispersed in a material for forming a conductive coat layer of the charging member and this enables achievement of the resolution of the problem that the charging member layer may change in electrical resistance with its service.